Optocoupler problems

[atom]

I'm (still :)) truing to get the core to work. I'm stuck in the same place, i can't get no INPUT (from computer to CORE). Nothing get's pass the optocoupler. I bought six of them. I've made the test on a vector board (http://www.ucapps.de/howtodebug/mbhp_core_opto_test.gif) and i get 1.5-1.7V in the place where there should be 0.10V (all 6 optocouplers). I also did a LED test on the input and the LED blinks whenever a midi message comes in (this is the test with the led before the opto).

It says on them 6N138 and they're white not black (but i guess that doesn't matter). Is there a way to check if midi is passing the optocoupler without removing the PIC, because if i keep removing and placing it back i will break it (i know myself to well). Is the loopback test a danger to the PIC if I leave it on ? Do you have any advice on how to debug the input and the opto in other ways?

any help is welocme.

[atom]

i went through the froum agian, i noticed someone mentioned the USB powered MIDI devices for computers have too small levels. Is that true? i have a Romio midi plugged to my mac, can this be an issue with no midi input in my Core?

[Dave_Wheeler]

Hi Atom,

The first test is an easy one. To check the stuff before the opto unplug it and connect and LED between pins 2 and 3 (cathode at 3) it should 'flicker' when midi in is present.

If this passes, then the problem is either the 6n138 or beyond. if it fails it is before.

Good Luck

Dave

[atom]

it flickers before, i just don't know how to check the midi right on the opot output, i know the rest works cause plugged my MIDI IN without the opto (the very hard bad way that should not be ever done), and i was able to begin programming so it worked. the problem is somewhere on the otpo itslef. i need to test that part.

what should i be getting and how (voltages, ohms) on the opto output when there are midi messages comming on it's input. that's what i want to find out. and can the lack of them on the input be caused by a too low signal on the midi interface (usb midi interface).

[Dave_Wheeler]

Hi Atom,

OK, this is good. If the LED flickers connected to where pins 2 and 3 go then the Midi input makes it to the opto and there is sufficient drive.

When you made the test circuit, what value pull up did you use ?? did you check the value with a meter ??

Now comes the silly question....have you got a good clean 5V supply and are you sure the opto is the right way up ? seems like a silly question but with some devices, pin 1 is not obvious

Dave

[atom]

I use a PSU used for powering cell phones in workshops, got it new. The voltage seems pretty stable up two a hundred part of a voltage 0.0x. As for the test circuit i'll run it again today, i used the same resisotrs as on the schematic, had to go to the shop to get them but they're exactly the same. As for the placement, i'll try switching it but i have the DOT that's suppose to point eh 1st pin. Like I said theese opto's that i have are white, but i think a spec for a perticular model stays the sme no matter what manufacturer makes them (or am i wrong?).

So there is no danger that the voltage that comes onto the opto is too low to drive it ?

[Dave_Wheeler]

OK, If the Opto has a dot, then that is pin 1 (some has a chamfered side). Inside the opto is basically an LED and a light controlled transistor junction so if the external LED flashes, so should the internal one. The test setup uses a current limited supply (through the 220r resistor) to test the opto so at this stage Midi is not part of the setup.

There are sometimes some minor differences between manufacturers but the 6n138 is a standard opto so you should not see any difference in this application.

The logic low voltage is listed as 0.1V but there is a maximum of 0.4V. As your tests show 1.5-1.7 I would guess that the pullup is too low a value, try a 10K instead

Dave